"We are using teargas on several fronts where youths are damaging stores and setting fire to garbage bins," a police official, who requested anonymity, said.

"It's been a year since police murdered the boy and the government which caused the murder has collapsed but nothing has changed in terms of police brutality," Panos Garganas, a university employee, told the Reuters news agency.

Al Jazeera's Barnaby Phillips, reporting from Athens, said: "There has been trouble during the last two or three hours very much centered around the university buildings in the centre of Athens.

"Under Greek law it is very difficult for the police to go into the university buildings and make arrests. Hardline groups were armed with many bricks, stones, Molotov cocktails and catapults, and they fought running battles with the police around these buildings.

"Meanwhile, the main march to commemorate the shooting of this 15-year-old boy, who was killed by the police last year, went through the city centre past the parliament building, and on the whole there things seemed to be peaceful.

"So, it's been a mixed picture - there has been sporadic trouble in parts of the Greek capital but the whole march itself was varied in tone," he said.

Police raid

On Saturday, Greek police arrested more than 150 people in Athens, to head off trouble on the anniversary.

Greece's government has warned it will have a zero tolerance policy towards violence [AFP]

The arrests took place after hundreds of people rallied in the central district of Exarchia, where Alexis Grigoropoulos was gunned down by a police officer on December 6 last year.